The present invention will be described by referring to a printed circuit board on which reception antenna are mounted but also the transmission/reception system, namely the “Front End Radio” circuit for wireless communication applications. However, it is obvious for a person skilled in the art that the present invention can be used on any printed circuit board requiring the use of test connectors.
Hence, as shown diagrammatically in FIG. 1 which shows a printed circuit board of the market on which an RF circuit (radiofrequency) is mounted, a test connector 1 is mounted on each of the printed lines 2 connecting a printed antenna such as antenna 3 to one of the inputs 4 of an RF circuit referenced 5. The test connectors that are in fact miniature connectors are automatically and definitively transferred on the printed circuit board, between the antennas and the RF circuit.
As shown in FIG. 2 of which the left-hand part relates to the operational mode and the right-hand part the test mode of a miniature connector, each connector comprises a mechanical switching system constituted mainly of two overlapping blades 10, 11, the blade 10 being offset on the RF circuit side input line whereas the blade 11 that overlaps the end of the blade 10 is an elastic blade offset and fixed to the output line on the antenna side.
The operation of such a connector is as follows. In operational mode, the two blades 10, 11 are in short-circuit and the transmission/reception signal (E/R) of the RF circuit is connected directly to the antenna in return for some insertion loss. In test mode, a coaxial probe referenced 12 in FIG. 2, equipped with a suitable adaptor, is plugged into the connector of the board. This has the effect of separating the blade 11 from the blade 10 by disconnecting in this manner the RF channel from the antenna channel and this enables the transmission/reception signal (E/R) of the RF circuit to be recovered in order for it to be measured.
Currently, the offset footprints of a test connector recommended by connector manufacturers have a shape such as the one shown in FIG. 3. Hence, in a more precise manner, on a part of the substrate 100 of the printed circuit board, the two metal feeder lines 101, 102 are realised. These two lines are found between two ground plane elements 103, 104. At the attachment site of the connector, each of the lines extends by a solder stud referenced 105, 106. Moreover, four solder studs 107 enable the connector to be attached to the board. A conductive material footprint 108 connects the two ground planes 103, 104 by passing between the solder studs.
As shown in FIG. 3, this footprint or pattern is connected by a metallised hole 109 to the lower ground plane of the printed board. Other metallised holes also connect the ground planes 103, 104 to the lower ground plane. The metallised holes enable the ground continuity to be provided between the lower and upper planes of the substrate.
The simulations conducted with test connectors of the market mounted on a footprint such as described with reference to FIG. 3, show that the transmission response (S21) is of the quasi low-pass type for the chosen operating band. Said response is due essentially to the form of the central parts of the connector that have been designed to meet two constraints, namely:                A mechanical constraint consisting in providing a perfect and reliable connection in operational mode of the two parts and a connection between the mobile part of the blades of the test connector in test mode.        Electrical constraints, namely to provide in particular in the operational mode, a perfect impedance matching to the access lines of characteristic impedance 50 ohms in the specified operating band.        